1. Field of the Invention
The present invention relates to a lamp unit for a vehicle headlamp, and more particularly, to a projector-type lamp unit which uses a light emitting device as a light source.
2. Background Art
In recent years, related art lamp units having a light emitting device as a light source, e.g., a light emitting diode, are increasingly being used in lamps such as vehicle headlamps.
For example, a related art projector-type lamp unit includes a projection lens disposed on an optical axis extending in a front-and-rear direction of a vehicle, a light emitting device disposed on a rear side of a rear focal point of the projection lens near the optical axis such that the light emitting device is oriented upward, and a reflector disposed to cover an upper side of the light emitting device to forwardly reflect light emitted from the light emitting device toward the optical axis (see, e.g., JP 2005-166590 A).
Such a lamp unit further includes a mirror member having an upwardly reflecting surface which upwardly reflects part of the light reflected from the reflector. The mirror member is disposed between the reflector and the projector lens such that a front edge of the upwardly reflecting surface passes through the rear focal point of the projection lens. The lamp unit is configured to form a low-beam light distribution pattern having a cutoff line along an upper edge thereof. The cutoff line is form as an inverted projection image of the front edge of the upwardly reflecting surface.
Another related art projector-type lamp unit includes a similar upwardly reflecting surface having a first horizontal surface extending on a self-lane side from an optical axis, an intermediate slope surface extending obliquely downward on an opposing-lane side from the optical axis, and a second horizontal surface extending on the opposing-lane side from a lower edge of the intermediate slope surface so as to be parallel to the first horizontal surface (see, e.g., JP 2006-114274 A).
By employing projector-type lamp units having the mirror member as described above, it is possible to increase a light flux utilization ratio for the light emitted from the light emitting device and, furthermore, to form the low-beam light distribution pattern with a clear cutoff line at the upper edge thereof.
Further, with the configuration in which the upper reflecting surface of the mirror member includes the first horizontal surface, the intermediate slope surface and the second horizontal surface as disclosed in JP 2006-114274 A, it is possible to form the low-beam light distribution pattern with a cutoff line having a opposing-lane cutoff line, a self-lane cutoff line extending at a level higher than the opposing-lane, and an oblique cutoff line connecting, on the self-lane side, the opposing-lane cutoff line and the self-lane cutoff line.
However, light reflected from the intermediate slope surface obliquely forms a light distribution pattern such that it partially overlaps with a light distribution pattern form by the second horizontal surface such that a dark portion is created between the light distribution pattern formed by the light reflected from the intermediate slope surface and a light distribution pattern formed by a light reflected from the first horizontal surface. Thus, the light distribution pattern formed by the light reflected from the mirror member tends to cause an unevenness of the low-beam light distribution pattern.